Involvement of estrogens in the regulation of granulosa cell aromatase activity

Androgens have been shown to enhance follicle-stimulating hormones (FSH) induced aromatase activity in cultured granulosa cells obtained from the ovaries of immature rats, however, aromatizable androgens are more effective than nonaromatizable androgens. The present study was designed to investigate the possibility that aromatization of androgens to estrogens is responsible for the greater effectiveness of aromatizable androgens. Granulosa cells were cultured during a 36-h induction period in the presence of FSH, FSH + testosterone, or FSH + dihydrotestosterone with or without 4-acetoxy-4-androstene-3,17-dione (4-acetoxy-A), an inhibitor of aromatase activity. Treatment with androgens enhanced aromatase activity measured as accumulation of estradiol-17 beta during a 6-h test period with testosterone added as substrate. The effects of both androgens on FSH-induced aromatase activity were blocked by 4-acetoxy-A. Presence of a high concentration of diethylstilbestrol (DES), a synthetic estrogen, during the induction period had a significant positive effect on FSH-induced estradiol-17 beta accumulation during the test period. All lower doses were ineffective. Nafoxidine, an antiestrogen known to inhibit binding of estrogens to their intracellular receptors, had no effect on enhancement of FSH-induced aromatase by testosterone. The results of these experiments suggest that estrogens synthesized by granulosa cells in culture are only partially responsible for the greater ability of testosterone to enhance FSH-induced aromatase activity compared with that of dihydrotestosterone (DHT). Other factors such as differential rates of androgen metabolism and receptor affinities are probably the major determinants of androgen potency.